The invention relates to a cover for radial rotors of turbo machines, which cover is divided in parts along a dividing plane. In preferred embodiments, the turbo machine is a gas turbine engine and the dividing plane extends radially of and includes the rotational axis of the radial rotor.
Such covers are frequently configured as undivided structures, the wall thickness of which is uniform over the whole perimeter. The reason for this is to ensure small gaps, as uniform as possible over the whole perimeter, between the radial rotor and the cover, such gaps having a decisive effect on the efficiency and surge line behaviour of highly stressed machines, e.g., radial compressors in aero gas turbines.
This mode of construction is admittedly disadvantageous for balancing and the smooth running of the machine in the case of multi-stage machines and where axial and radial stages are combined within one machine component. Also, there are disadvantages with regard to the manufacturing and assembly costs for such undivided one-piece cover structures.
Covers are also known which are separable along a dividing or meridian plane. However, previously contemplated designs exhibit shortcomings in that non-uniform distribution of material around the perimeter--resulting, for instance, from material massed in the dividing plane at connecting flanges or the like--provides variable rigidity and variable thermal capacities around the perimeter of the cover.
Particularly in non-steady operating conditions, this variable rigidity and variable thermal capacity leads to deformation in the individual meridian planes (radial planes including the rotor axis of rotation) of the cover and consequently to negative effects on the performance and operating behavior of the turbo machine in question.
An important object of the invention is to eliminate the above-mentioned disadvantages and to devise a cover arrangement which is separable in one meridian dividing plane for the radial rotors being covered and which will ensure a constant radial gap between the radial rotor and the cover under all operating conditions.
To solve the given tasks, a primary proposal in the invention is that, starting from the meridian or dividing plane, supporting ribs are attached on the outside wall of the cover in several other meridian planes spaced evenly around the perimeter; the shape of these ribs corresponding to the flanges in the dividing plane.
The area moment of inertia and thermal storage capacity of the ribs preferably have corresponding values for the flanges in the dividing plane. At the same time, bending resistance of the ribs is preferably matched to the flanges in the dividing plane to guarantee constant gaps around the perimeter, above all under steady-state operating conditions. Thermal storage capacity of the ribs matched to the flanges in the dividing plane provides for constant gaps around the perimeter, above all under non-steady-state operating conditions, e.g., when load changes are abrupt.
In a further elaboration of preferred embodiments of the invention, the attached ribs are combined with the flanges to form a type of skeleton, so that the part of the cover directly adjacent the rotor is practically kept free from structural support functions.
In a further elaboration of preferred embodiments of the invention, the cover is connected with the turbo machine casing by a number of radially disposed bolts. By this means, the cover is kept completely free from forces and deformations resulting from the structure of the machine. This automatically leads to a reduction of the gap variations between rotor and cover.
If, in addition, the thermal storage capacity of the cover is matched to that of the rotor, the gaps in operation can be kept small even when load changes are abrupt.
In particularly preferred embodiments, the connecting flanges and the rib members or portions form a symmetric configuration around the periphery of the rotor.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.